Still winless six games into the season, the Red Bulls knew how important a victory was, how desperately they needed three points against Philadelphia. And a day after star Tim Cahill proclaimed a victory was in the cards, they went out and finally got one, holding on for a 2-1, 10-man escape against the rival Union.

“It was just one of them games. That’s it. You have to stand up and be counted. I said it: Our season starts [Wednesday]. If it doesn’t we put ourselves in a real difficult position. But we showed it. When you put belief in other players and we start believing we’ll score goals,’’ Cahill said. “The boys have got to believe in themselves and belief starts [Wednesday].’’

“I said to [coach Mike Petke] before we’re going to win this game. I was 100 percent sure. … We just have to believe in ourselves because we’re a great football team. We finally found our feet … and found the three points. I said this is going to be the start of our season and it is, because the win is going to take us forward.’’

After starting off winless in their first half dozen games — the third-worst start ever for a Supporters’ Shield holder — the Red Bulls (1-2-4) finally got that victory. But they had to work for it, getting goals from captain Thierry Henry and from Lloyd Sam, then having to overcome a 78th minute red card to hold on.

“But what do you do, give up? Or carry on playing hard? And that’s what we did,’’ Henry said of the winless start. “What do you do, give up? That’s not the way to do it: You come back and try to play hard and that’s what we did.’’

Midfielder Eric Alexander — who is naturally right-footed and got his first-ever start with New York on the left — got two assists.

In the 57th minute, he rolled the ball down the line to an overlapping Miller. The Costa Rican left back cut it into the box to Henry, who was left wide open 12 yards out and put it past GK Zac MacMath.

“We kept on going, playing down the wings, and Roy Miler found me in the box,” Henry said.

They got a much-needed insurance tally in the 67th minute. Alexander managed to get to the endline and chipped the ball in to Sam, who beat Cahill to the ball to headed it home.

They needed that 2-0 lead, holding on for dear life the rest of the way.

Ibrahim Sekagya went to the ground to block Maurice Edu’s shot in the box, and was whistled for a handball when it deflected off his right arm. He was sent off, and former Red Bull Sebastien Le Toux calmly beat keeper Luis Robles to halve the lead in the 80th minute.

Petke brought defender Armando in for Wright-Phillips to help the 10-man Red Bulls kill off the rest of the game.